Methods and devices for determining the position of at least two subsystems which are moveable relative to one another have been known for a long time. One conventional approach involves the imaging of a code onto a detecting component, wherein the imaging is generally effected using optical means, such as e.g. LEDs and/or lasers. The function of position determination and, in particular, the accuracy thereof are dependent on the design and arrangement of the code and also the imaging means.
The determination of directions, angles and lengths as positions and also of distances is required in many areas of application such as, for example, geodetic and industrial measurement. Development in position measurement technology lead via mechanical reading operations to fully automated position measurement according to the current prior art.
Known scanning methods are electronic-magnetic, electronic and optoelectronic methods. The following explanations concern optoelectronic scanning devices.
Conventional optoelectronic position measurement sensors—known e.g. from DE 83 02 799 U1—for determining a distance or an angle about an axis have a code carrier and a detection unit having a multiplicity of light-sensitive receiving regions for receiving part of the optical radiation, wherein the code carrier and the detection unit are rotatable relative to one another. The optical detector is a photodetector, for example. The code carrier is embodied generally as a rod or circular disk, if appropriate also as an annulus, and carries on one side an optically detectable position code, an excerpt from which is imaged onto the detection unit by an illumination device. In general, the code carrier is embodied in a movable fashion in this case. However, it is also possible to realize an embodiment in which the code carrier is stationary and the detector moves.
CH 522 876 discloses arranging a diaphragm between the code carrier and the detection unit. It has been found, however, that such arrangements are extremely difficult to manufacture because the detection unit and the diaphragm are very small and, moreover, have to be aligned precisely with respect to one another in order that the desired radiation components are detected by the detection unit. In this case, there are conflicting requirements made of the size of the diaphragm apertures or the slot of the diaphragm, the width of the detector area and the distance between detector and diaphragm. By means of the diaphragm, obliquely incident light is shielded and, consequently, the solid angle detected by the detector is restricted. In this case, detector or pixel width and slot width and also diaphragm distance are in a mutual relationship. Given a large detector width, the slot has to be kept narrow or the diaphragm distance has to be chosen to be large, in order to bring about a corresponding restriction of the solid angle. However, a reduction of the slot width also reduces the quantity of light actually available, and an increase in the diaphragm distance enlarges the overall construction.